Use the standard normal distribution or the​ t-distribution to construct a 90​% confidence interval for the population mean. Justify your decision. If neither distribution can be​ used, explain why. Interpret the results.   In a random sample of 12 mortgage​ institutions, the mean interest rate was 3.57​% and the standard deviation was 0.38​%. Assume the interest rates are normally distributed.   Which distribution should be used to construct the confidence​ interval?     A. Use a normal distribution because n<30 and the interest rates are normally distributed.   B. Use a​ t-distribution because the interest rates are normally distributed and σ is known.   C. Use a normal distribution because the interest rates are normally distributed and σ is known.   D. Use a​ t-distribution because it is a random​ sample, σ is​ unknown, and the interest rates are normally distributed.   E. Cannot use the standard normal distribution or the​ t-distribution because σ is​ unknown, n<30​, and the interest rates are not normally distributed.

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Use the standard normal distribution or the​ t-distribution to construct a
90​%
confidence interval for the population mean. Justify your decision. If neither distribution can be​ used, explain why. Interpret the results.
 
In a random sample of
12
mortgage​ institutions, the mean interest rate was
3.57​%
and the standard deviation was
0.38​%.
Assume the interest rates are normally distributed.
 
Which distribution should be used to construct the confidence​ interval?
 
 
A.
Use a normal distribution because
n<30
and the interest rates are normally distributed.
 
B.
Use a​ t-distribution because the interest rates are normally distributed and
σ
is known.
 
C.
Use a normal distribution because the interest rates are normally distributed and
σ
is known.
 
D.
Use a​ t-distribution because it is a random​ sample,
σ
is​ unknown, and the interest rates are normally distributed.
 
E.
Cannot use the standard normal distribution or the​ t-distribution because
σ
is​ unknown,
n<30​,
and the interest rates are not normally distributed.
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